Endogenous oxidative injury to cellular DNA may be induced by exogenous chemical toxicity and/or inflammation and has been speculated to contribute to mutation frequency (MF) and mutations that may be fixed and clonally expanded (multistage carcinogenesis) by induced cellular proliferation. Our goal is to determine the mutation frequency and to characterize mutations in transgenic ZAP/lacIq mice (C57B1/6 background) using a lambda shuttle vector after treatment with selected genotoxic or non-genotoxic chemicals that induce hyperplasia with and without associated inflammation as a model for genomic DNA damage. The target transgene is recovered from treated transgenic mice by exposing the mouse genomic DNA to lambda in vitro packaging extracts, infecting repair deficient host E. coli, and culturing. Phage with mutations in the lacI target gene form colored plaques, while those with non-mutated target genes form colorless plaques. We have initiated these studies by determining mutation frequency in liver after ethylnitrosourea or vehicle exposure and induction of rapid hepatocellular proliferation following 2/3 partial hepatectomy. Ablated liver served as the To and untreated control. After 8 days (100% restoration of liver mass) EtNU followed by hepatectomy increased MF 4.4X compared to ~1.9 or 1.7X for hepatectomy alone or EtNU and sham hepatectomy. Additional studies performed with benzene, p-cresidine, 1,2,3-trichloropropane and 4-vinyl-1-cyclohexene diepoxide are undergoing analysis. Using this research strategy we expect to be able to provide insight on chemical and/or endogenous oxidative damage to DNA and this possible mechanism of carcinogenesis.